Methods selecting modulation/coding schemes mapped to multiple mimo layers and related user equipment

ABSTRACT

A method of operating a user equipment communicating with a base station of a radio access network may include selecting a multiple-input-multiple-output, MIMO, rank and a MIMO precoding entity from a codebook of MIMO precoding entities for a downlink communication from the base station to the user equipment. A modulation/coding scheme to be mapped to first and second MIMO layers of the downlink communication may be selected using the MIMO precoding entity. Channel quality information may be communicated identifying the MIMO precoding entity and the modulation/coding scheme from the user equipment to the base station. Related user equipment nodes are also discussed.

RELATED APPLICATION

The present application claims the benefit of priority from U.S.Provisional Application No. 61/559,872 filed Nov. 15, 2011, thedisclosure of which is hereby incorporated herein in its entirety byreference.

TECHNICAL FIELD

The present disclosure is directed to wireless communications and, moreparticularly, to multiple-input-multiple-output (MIMO) wirelesscommunications and related network nodes and wireless terminals.

BACKGROUND

In a typical cellular radio system, wireless terminals (also referred toas user equipment unit nodes, UEs, and/or mobile stations) communicatevia a radio access network (RAN) with one or more core networks. The RANcovers a geographical area which is divided into cell areas, with eachcell area being served by a radio base station (also referred to as aRAN node, a “NodeB”, and/or enhanced NodeB “eNodeB”). A cell area is ageographical area where radio coverage is provided by the base stationequipment at a base station site. The base stations communicate throughradio communication channels with UEs within range of the base stations.

Multi-antenna techniques can significantly increase capacity, datarates, and/or reliability of a wireless communication system asdiscussed, for example, by Telatar in “Capacity Of Multi-AntennaGaussian Channels” (European Transactions On Telecommunications, Vol.10, pp. 585-595, November 1999). Performance may be improved if both thetransmitter and the receiver for a base station sector are equipped withmultiple antennas (e.g., an sector antenna array) to provide amultiple-input multiple-output (MIMO) communication channel(s) for thebase station sector. Such systems and/or related techniques are commonlyreferred to as MIMO. The LTE standard is currently evolving withenhanced MIMO support and MIMO antenna deployments. A spatialmultiplexing mode is provided for relatively high data rates in morefavorable channel conditions, and a transmit diversity mode is providedfor relatively high reliability (at lower data rates) in less favorablechannel conditions.

In a downlink from a base station transmitting from a sector antennaarray over a MIMO channel to a wireless terminal in the sector, forexample, spatial multiplexing (or SM) may allow the simultaneoustransmission of multiple symbol streams over the same frequency from thebase station sector antenna array for the sector. Stated in other words,multiple symbol streams may be transmitted from the base station sectorantenna array for the sector to the wireless terminal over the samedownlink transmission time interval (TTI) and/or time/frequency resourceelement (TFRE) to provide an increased data rate. In a downlink from thesame base station sector transmitting from the same sector antenna arrayto the same wireless terminal, transmit diversity (e.g., usingspace-time codes) may allow the simultaneous transmission of the samesymbol stream over the same frequency from different antennas of thebase station sector antenna array. Stated in other words, the samesymbol stream may be transmitted from different antennas of the basestation sector antenna array to the wireless terminal over the sametime/frequency resource element (TFRE) to provide increased reliabilityof reception at the wireless terminal due to transmit diversity gain.

Four layer MIMO transmission (4Tx) schemes are proposed forHigh-Speed-Downlink-Packet-Access (HSDPA) within Third GenerationPartnership Project (3GPP) standardization as disclosed, for example, in3GPP RP-111393 (“New WI: Four Branch MIMO Transmission For HSDPA,” 3GPPTSG-RAN meeting # 53, Fukuoka, Japan, Sept. 13-16, 2011) and 3GPPR1-111763 (“4-branch MIMO for HSDPA,” 3GPP TAG RAN WG1 Meeting #5,Barcelona, Spain, May 9-13, 2011), the disclosures of both of which arehereby incorporated herein in their entireties by reference.Accordingly, up to 4 layers of information/data may be transmitted inparallel using a same TTI/TFRE when using 4-branch MIMO transmission.

The number of codewords supported by 4 branch MIMO is one issueregarding implementation of 4 branch MIMO. Contributions discussingpossible configurations for 4×4 MIMO include 3GPP R1-113432 (“4×4 DLMIMO HS-DPCCH Design,” 3GPP TSG RAN WG1 Meeting #66bis, Zhuhai, P. R.China, Oct. 10-14, 2011), 3GPP R1-112979 (“Discussion on 4-Branch MIMODesign Options,” 3GPP TSG-RAN WG1 Meeting #66bis, Zhuhia, China, Oct.10-14, 2011), and 3GPP R1-113360 (“Codeword to Layer MappingAlternatives For DL 4 Branch MIMO,” 3GPP TSG-RAN WG1 Meeting #66bis,Zhuhia, China, Oct. 10-14, 2011), the disclosures of which are herebyincorporated herein in their entireties by reference.

Among proposed configurations for 4×4 MIMO, configurations for 4codeword 4×4 MIMO and 2 codeword 4×4 MIMO are likely candidates forfurther investigation. In 3GPP R1-114290 (“Number of Supported Codewordsfor 4-branch MIMO,” 3GPP TSG RAN WG1 Meeting #67, San Francisco, USA,Nov. 14-18, 2011), a 2 codeword 4 branch MIMO is proposed forstandardization, and the disclosure of 3GPP R1-114290 is herebyincorporated herein in its entirety by reference.

Channel quality information for a 4×4 MIMO system, however, may bedifficult to compute and/or report.

SUMMARY

It may therefore be an object to address at least some of the abovementioned disadvantages and/or to improve performance in a wirelesscommunication system.

According to some embodiments, a method of operating user equipmentcommunicating with a base station of a radio access network may includeselecting a multiple-input-multiple-output (MIMO) rank and a MIMOprecoding entity from a codebook of MIMO precoding entities for adownlink communication from the base station to the user equipment. Amodulation/coding scheme may be selected to be mapped to first andsecond MIMO layers of the downlink communication using the MIMOprecoding entity. Channel quality information (CQI) identifying the MIMOprecoding entity and the modulation/coding scheme may be communicatedfrom the user equipment to the base station.

The modulation/coding scheme may be a first modulation/coding scheme.Responsive to selecting the MIMO precoding entity, a secondmodulation/coding scheme may be selected to be mapped to a third MIMOlayer of the downlink communication using the MIMO precoding entity,with the channel quality information including the secondmodulation/coding scheme. For rank 3, the first modulation/coding schememay be mapped to two different MIMO downlink transmission/receptionlayers, and the second modulation/coding scheme may be mapped to a thirdMIMO downlink transmission/reception layer.

The modulation/coding scheme may be a first modulation/coding scheme.Responsive to selecting the MIMO precoding entity, a secondmodulation/coding scheme may be selected to be mapped to third andfourth MIMO layers of the downlink communication using the MIMOprecoding entity, with the channel quality information including thesecond modulation/coding scheme. For rank 4, the first modulation/codingscheme may be mapped to two different MIMO downlinktransmission/reception layers, and the second modulation/coding schememay be mapped to two other MIMO downlink transmission/reception layers.

Estimates of the downlink channel may be provided responsive to pilotsignals received from the base station, and respective first and secondsignal strengths may be estimated for the first and second layers of theMIMO precoding entity, wherein selecting the modulation/coding schemeincludes selecting the modulation/coding scheme responsive to a functionof first and second signal strengths. Selecting the modulation/codingscheme may include selecting the modulation/coding scheme responsive toan average of the first and second signal strengths, responsive to amaximum of the first and second signal strengths, and/or responsive to aminimum of the first and second signal strengths.

Channel estimates may be provided for a downlink channel from the basestation to the user equipment. Signal strengths may be estimated for theMIMO layers for the precoding entities of the codebook using the channelestimates. Capacities for the precoding entities of the codebook may beestimated using the signal strengths, wherein selecting the MIMOprecoding entity includes selecting the MIMO precoding entity responsiveto the capacities. Moreover, selecting may include selecting themodulation/coding scheme responsive to a function of first and secondsignal strengths estimated for the first and second MIMO layers for theprecoding entity using the channel estimates. In addition, selecting themodulation/coding scheme may include selecting the modulation/codingscheme responsive to an average of the first and second signalstrengths, responsive to a maximum of the first and second signalstrengths, and/or responsive to a minimum of the first and second signalstrengths.

A respective modulation/coding scheme may be selected for each of thelayers of each of the MIMO precoding entities of the codebook. Arespective layer efficiency may be calculated for each of the layers ofeach of the MIMO precoding entities of the codebook responsive to therespective modulation/coding schemes. A respective precoding entityefficiency may be provided for each of the MIMO precoding entities ofthe codebook responsive to the layer efficiencies of the respective MIMOprecoding entities. Moreover, selecting the MIMO precoding entity mayinclude selecting the MIMO precoding entity responsive to the precodingentity efficiencies.

Providing the respective precoding entity efficiency for the selectedMIMO precoding entity may include providing the respective precodingentity efficiency for the selected MIMO precoding entity responsive to afunction of first and second layer efficiencies for the first and secondMIMO layers of the selected MIMO precoding entity.

Providing the respective precoding entity efficiency for the selectedMIMO precoding entity responsive to a function of first and second layerefficiencies may include providing the respective precoding entityefficiency responsive to a maximum of the first and second layerefficiencies. Selecting the modulation/coding scheme to be mapped to thefirst and second MIMO layers of the selected precoding entity mayinclude selecting one of a first modulation/coding scheme of the firstlayer of the selected MIMO precoding entity and a secondmodulation/coding scheme of the second layer of the selected MIMOprecoding entity corresponding to the maximum of the first and secondlayer efficiencies.

Providing the respective precoding entity efficiency for the selectedMIMO precoding entity responsive to a function of first and second layerefficiencies may include providing the respective precoding entityefficiency responsive to a minimum of the first and second layerefficiencies. Selecting the modulation/coding scheme to be mapped to thefirst and second MIMO layers of the selected precoding entity mayinclude selecting one of a first modulation/coding scheme of the firstlayer of the selected MIMO precoding entity and a secondmodulation/coding scheme of the second layer of the selected MIMOprecoding entity corresponding to the minimum of the first and secondlayer efficiencies.

Estimates of the downlink channel may be provided responsive to pilotsignals received from the base station, and a respective signal strengthmay be estimated for each layer of each of the MIMO precoding entitiesof the codebook using the estimates of the downlink channel. Moreover,selecting may include selecting the respective modulation/coding schemefor each of the layers of each of the MIMO precoding entities of thecodebook responsive to the respective signal strengths.

According to some other embodiments, user equipment may be configured tocommunicate with a base station of a radio access network. The userequipment may include a transceiver configured to receive communicationsfrom the base station and to transmit communications to the basestation, and a processor coupled to the transceiver. The processor maybe configured to select a multiple-input-multiple-output (MIMO) rank anda MIMO precoding entity from a codebook of MIMO precoding entities for adownlink communication from the base station to the user equipment, toselect a modulation/coding scheme to be mapped to first and second MIMOlayers of the downlink communication using the MIMO precoding entity,and to communicate channel quality information identifying the MIMOprecoding entity and the modulation/coding scheme through thetransceiver to the base station.

The processor may be further configured to provide estimates of thedownlink channel responsive to pilot signals received from the basestation, to estimate respective first and second signal strengths forthe first and second layers of the MIMO precoding entity, and to selectthe modulation/coding scheme responsive to a function of first andsecond signal strengths.

The processor may be further configured to provide channel estimates fora downlink channel from the base station to the user equipment, toestimate signal strengths for the MIMO layers for the precoding entitiesof the codebook using the channel estimates, to estimate capacities forthe precoding entities of the codebook using the signal strengths, toselect the MIMO precoding entity responsive to the capacities, and toselect the modulation/coding scheme responsive to a function of firstand second signal strengths estimated for the first and second MIMOlayers for the precoding entity using the channel estimates.

The processor may be further configured to select a respectivemodulation/coding scheme for each of the layers of each of the MIMOprecoding entities of the codebook, to calculate a respective layerefficiency for each of the layers of each of the MIMO precoding entitiesof the codebook responsive to the respective modulation/coding schemes,to provide a respective precoding entity efficiency for each of the MIMOprecoding entities of the codebook responsive to the layer efficienciesof the respective MIMO precoding entities, and to select the MIMOprecoding entity responsive to the precoding entity efficiencies.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the disclosure and are incorporated in and constitute apart of this application, illustrate certain non-limiting embodiment(s)of the invention. In the drawings:

FIG. 1 is a block diagram of a communication system that is configuredaccording to some embodiments;

FIG. 2 is a block diagram illustrating a base station and a wirelessterminal according to some embodiments of FIG. 1;

FIG. 3 is a block diagram illustrating elements/functionalities of basestation processors according to some embodiments of FIG. 2;

FIG. 4 is a block diagram illustrating elements/functionalities ofwireless terminal processors according to some embodiments of FIG. 2;

FIG. 5 is a flow chart illustrating operations of selecting channelquality information according to some embodiments of the presentinvention;

FIG. 6 is a flow chart illustrating operations of selecting channelquality information according to some embodiments of FIG. 5;

FIGS. 7A to 7D are tables illustrating a matrix of signal to noiseratios (SNRs) for precoding vector layers according to some embodimentsof the present invention;

FIGS. 8A to 8D are tables illustrating a matrix of capacities ofprecoding vectors of FIGS. 7A to 7D;

FIG. 9 is a table illustrating modulation/coding scheme selectionaccording to some embodiments of FIG. 5;

FIG. 10 is a flow chart illustrating operations of selecting channelquality information according to some embodiments of FIG. 6;

FIGS. 11A and 11B are flow charts illustrating operations of providingprecoder vector efficiencies according to some embodiments of FIG. 10;

FIGS. 12A and 12B are flow charts illustrating operations of selectingmodulation/coding schemes according to some embodiments of FIG. 10;

FIGS. 13A to 13D are tables illustrating a matrix of modulation/codingschemes corresponding to signal to noise ratios of FIGS. 7A to 7D;

FIGS. 14A to 14D are tables illustrating a matrix of spectralefficiencies corresponding to modulation/coding schemes of FIGS. 13A to13D;

FIGS. 15A to 15D are tables illustrating a matrix of spectralefficiencies corresponding to precoding vectors;

FIG. 16 is a graph illustrating link level performance of 4×4 MIMOdownlink transmissions using 2 codewords and using 4 codewords;

FIG. 17 is a block diagram illustrating elements/functionalities of basestation processors according to some other embodiments of the presentinvention;

FIG. 18 is a table illustrating mappings of modulated codewords todownlink transmission layers according to some embodiments of thepresent invention; and

FIGS. 19 and 20 are block diagrams illustrating elements/functionalitiesof UE processors according to some embodiments of the present invention.

DETAILED DESCRIPTION

The invention will now be described more fully hereinafter withreference to the accompanying drawings, in which examples of embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the present invention to those skilled in the art.It should also be noted that these embodiments are not mutuallyexclusive. Components from one embodiment may be tacitly assumed to bepresent/used in another embodiment.

For purposes of illustration and explanation only, these and otherembodiments of the present invention are described herein in the contextof operating in a RAN that communicates over radio communicationchannels with wireless terminals (also referred to as user equipmentnodes or UEs). It will be understood, however, that the presentinvention is not limited to such embodiments and may be embodiedgenerally in any type of communication network. As used herein, awireless terminal (also referred to as a UE) can include any device thatreceives data from a communication network, and may include, but is notlimited to, a mobile telephone (“cellular” telephone), laptop/portablecomputer, pocket computer, hand-held computer, and/or desktop computer.

In some embodiments of a RAN, several base stations can be connected(e.g., by landlines or radio channels) to a radio network controller(RNC). The radio network controller, also sometimes termed a basestation controller (BSC), supervises and coordinates various activitiesof the plural base stations connected thereto. The radio networkcontroller is typically connected to one or more core networks.

The Universal Mobile Telecommunications System (UMTS) is a thirdgeneration mobile communication system, which evolved from the GlobalSystem for Mobile Communications (GSM), and is intended to provideimproved mobile communication services based on Wideband Code DivisionMultiple Access (WCDMA) technology. UTRAN, short for UMTS TerrestrialRadio Access Network, is a collective term for the Node B's and RadioNetwork Controllers which make up the UMTS radio access network. Thus,UTRAN is essentially a radio access network using wideband code divisionmultiple access for UEs.

The Third Generation Partnership Project (3GPP) has undertaken tofurther evolve the UTRAN and GSM based radio access networktechnologies. In this regard, specifications for the Evolved UniversalTerrestrial Radio Access Network (E-UTRAN) are ongoing within 3GPP. TheEvolved Universal Terrestrial Radio Access Network (E-UTRAN) comprisesthe Long Term Evolution (LTE) and System Architecture Evolution (SAE).

Note that although terminology from 3GPP (3^(rd) Generation PartnershipProject) LTE (Long Term Evolution) is used in this disclosure toexemplify embodiments of the invention, this should not be seen aslimiting the scope of the invention to only these systems. Otherwireless systems, including WCDMA (Wideband Code Division MultipleAccess), WiMax (Worldwide Interoperability for Microwave Access), UMB(Ultra Mobile Broadband), HSDPA (High-Speed Downlink Packet Access), GSM(Global System for Mobile Communications), etc., may also benefit fromexploiting embodiments of the present invention disclosed herein.

Also note that terminology such as base station (also referred to asNodeB, eNodeB, or Evolved Node B) and wireless terminal (also referredto as UE or User Equipment) should be considering non-limiting and doesnot imply a certain hierarchical relation between the two. In general abase station (e.g., an “NodeB”) and a wireless terminal (e.g., a “UE”)may be considered as examples of respective different communicationsdevices that communicate with each other over a wireless radio channel.While embodiments discussed herein may focus on wireless transmissionsin a downlink from an NodeB to a UE, embodiments of the invention mayalso be applied, for example, in the uplink.

FIG. 1 is a block diagram of a communication system that is configuredto operate according to some embodiments of the present invention. Anexample RAN 60 is shown that may be a Long Term Evolution (LTE) RAN.Radio base stations (e.g., NodeBs) 100 may be connected directly to oneor more core networks 70, and/or radio base stations 100 may be coupledto core networks 70 through one or more radio network controllers (RNC).In some embodiments, functionality of a radio network controller(s) maybe performed by radio base stations 100. Radio base stations 100communicate over wireless channels 300 with wireless terminals (alsoreferred to as user equipment nodes or UEs) 200 that are within theirrespective communication service cells (also referred to as coverageareas). The radio base stations 100 can communicate with one anotherthrough an X2 interface and with the core network(s) 70 through S1interfaces, as is well known to one who is skilled in the art.

FIG. 2 is a block diagram of a base station 100 and a wireless terminal200 of FIG. 1 in communication over wireless channel 300 according tosome embodiments of the present invention. As shown, base station 100may include transceiver 109 coupled between processor 101 and antennaarray 117 (including multiple antennas), and memory 118 coupled toprocessor 101. Moreover, wireless terminal 200 may include transceiver209 coupled between antenna array 217 and processor 201, and userinterface 221 and memory 218 may be coupled to processor 201.Accordingly, base station processor 101 may transmit communicationsthrough transceiver 109 and antenna array 117 for reception at wirelessterminal processor 201 through antenna array 217 and transceiver 209. Inthe other direction, wireless terminal processor 201 may transmitcommunications through transceiver 209 and antenna array 217 forreception at base station processor 101 through antenna array 117 andtransceiver 109. To support up to 4-branch MIMO (allowing paralleltransmission of 4 layers/streams of data using a same TFRE), each ofantenna arrays 117 and 217 may include four (or more) antenna elements.Wireless terminal 200 of FIG. 2, for example, may be a cellularradiotelephone, a smart phone, a laptop/netbook/tablet/handheldcomputer, or any other device providing wireless communications. Userinterface 211, for example, may include a visual display such as anliquid crystal display, a touch sensitive visual display, a keypad, aspeaker, a microphone, etc.

For MIMO downlink transmissions from RAN 60 to wireless terminal 200, acodebook of precoding vectors (known at both RAN 60 and wirelessterminal 200) is used to precode (e.g., to apply precoding weights to)the different data layers (data streams) that are transmitted inparallel from a sector antenna array(s) to the wireless terminal 200during a same TFRE, and to decode the data layers (data streams)received in parallel during the same TFRE at wireless terminal 200. Thesame codebook of precoding vectors may be stored in wireless terminalmemory 218 and in base station memory 118. Moreover, wireless terminal200 may estimate characteristics of each downlink channel to generatechannel quality information (CQI), and CQI feedback from wirelessterminal 200 may be transmitted to base station 100. This CQI feedbackmay then be used by the base station processor 101 to select:transmission rank (i.e., a number of data layers/streams to betransmitted during a subsequent TFRE); transport data block length(s);channel code rate(s) to be used to channel encode different transportdata blocks; modulation order(s) defining a number of bits mapped to amodulated symbol; symbol to layer mapping schemes; and/or precodingvectors for respective downlink transmissions to the wireless terminal200.

By way of example, base station antenna array 117 may include 4 antennasand wireless terminal antenna array 217 may include four antennas sothat wireless terminal 200 may receive up to four downlink data layers(data streams) from base station antenna array 117 during MIMOcommunications. In this example, the precoding codebook may include rank1 precoding vectors (used when transmitting one downlink data streamfrom a base station sector antenna array 117 to wireless terminal 200),rank 2 precoding vectors (used when transmitting two downlink datastreams from a base station sector antenna array 117 to wirelessterminal 200), rank 3 precoding vectors (used when transmitting threedownlink data streams from a base station sector antenna array 117 towireless terminal 200), and rank 4 precoding vectors (used whentransmitting four downlink data streams from a base station sectorantenna array 117 to wireless terminal 200). Precoding vectors may alsobe referred to, for example, as precoding codebook entries, precodingcodewords, and/or precoding matrices.

Wireless terminal 200 may transmit CQI/PCI information (over uplinkcontrol channel HS-DPCCH) including a rank indicator RI(requesting/recommending a MIMO transmission rank), a precoding controlindex PCI (requesting/recommending a precoding vector, also referred toas a precoding index), and a modulation/coding scheme (MCS) forsubsequent downlink transmissions from base station 100 to wirelessterminal 200. Base station processor 101 may select therequested/recommended MIMO rank/vector and/or MCS and/or a differentMIMO rank/vector and/or MCS, and base station 100 may indentify theselected MIMO rank/vector and/or MCS in downlink signaling transmittedto wireless terminal 200. Base station 100 may then transmit one or moretransport data blocks using respective MIMO layers/streams over thedownlink channel in a subsequent TTI/TFRE in accordance with theselected MIMO rank/vector and/or MCS as downlink traffic.

FIG. 3 is block diagram illustrating elements/functionalities of basestation processor 101 of FIG. 2 supporting two codeword MIMO with 2channel encoders and up to four rank MIMO downlink transmissionaccording to some embodiments. According to embodiments of FIG. 3, fourchannel encoders CE1, CE2, CE3, and CE4 may be provided for up to fourstreams of transport data blocks B1, B2, B3, and B4, with symbols ofdata input streams for wireless terminal 200 being mapped to respectivedata transmission layer/streams X1, X2, X3, and X4. As shown, processor101 may include transport data block generator 401, channel encoder 403,modulator 405, layer mapper 407, spreader/scrambler 409, and layerprecoder 411. In embodiments of FIG. 4, channel encoder 403 may includechannel encoders CE1, CE2, CE3, and CE4 for four streams of transportdata blocks B1, B2, B3, and B4, modulator 405 may includeinterleavers/modulators IM1, IM2, IM3, and IM4, and layer mapper 407 maybe configured to map resulting symbols of the streams to respective MIMOlayers (streams) X1, X2, X3, and X4 as discussed in greater detailbelow. Moreover, adaptive controller 415 may be configured to controltransport data block generator 401, channel encoder 403, modulator 405,layer mapper 407, spreader/scrambler 409, and/or layer precoder 411responsive to channel quality information (CQI) received as feedbackfrom wireless terminal 200. According to some embodiments discussedherein, layer mapper 407 may perform a one-to-one mapping. Accordingly,symbols from interleavers/modulators IM1, IM2, IM3, and IM4 may each mapdirectly to respective MIMO layers (streams) X1, X2, X3, and X4.

Base station processor 101, for example, may receive input data (e.g.,from core network 70, from another base station, etc.) for transmissionto wireless terminal 200, and transport data block generator 401(including transport data block data generators TB1, TB2, TB3, and TB4)may provide a single stream of data blocks (for rank 1 transmissions),two streams of data blocks (for rank 2 transmissions), three streams ofdata (for rank 3 transmissions), and four streams of data (for rank 4transmissions).

For rank 1 transmissions (providing only 1 MIMO layer/stream), all inputdata may be processed through transport data block generator TB1 toprovide a single stream of transport data blocks B1 (includingindividual transport data blocks b1-1, b1-2, b1-3, etc.) without usingtransport data block generators TB2, TB3, and TB4 and without generatingother layers/streams of transport data blocks B2, B3, and B4. For rank 2transmissions (providing 2 MIMO layers/streams), transport data blockgenerator TB1 may generate a layer/stream of transport data blocks B1(including individual transport data blocks b1-1, b1-2, b1-3, etc.), andtransport data block generator TB2 may generate a stream of transportdata blocks B2 (including individual transport data blocks b2-1, b2-2,b2-3, etc.), without using transport data block generators TB3 and TB4and without generating layers/streams of transport data blocks B3 andB4. For rank 3 transmissions (providing 3 MIMO layers/streams),transport data block generator TB1 may generate a layer/stream oftransport data blocks B1 (including individual transport data blocksb1-1, b1-2, b1-3, etc.), transport data block generator TB2 may generatea stream of transport data blocks B2 (including individual transportdata blocks b2-1, b2-2, b2-3, etc.), and transport data block generatorTB3 may generate a stream of transport data blocks B 3 (includingindividual transport data blocks b3-1, b3-2, b3-3, etc.) without usingtransport data block generator TB4 and without generating a fourthlayer/stream of transport data block B4.

Channel encoder 403 (including channel encoders CE1, CE2, CE3, and CE4)may encode the stream/streams of data blocks B1, B2, B3, and/or B4generated by transport data block generator 401 to provide respectivestreams of codewords CW1 (including individual codewords cw1-1, cw1-2,cw1-3, etc.), CW2 (including individual codewords cw2-1, cw2-2, cw2-3,etc.), CW3 (including individual codewords cw3-1, cw3-2, cw3-3, etc.),and CW4 (including individual codewords cw4-1, cw4-2, cw4-3, etc.), forexample, using turbo coding, convolutional coding, etc. Moreover, codingcharacteristics (e.g., coding rates) applied by channel encoders CE1,CE2, CE3, and CE4 may be separately determined by adaptive controller415 responsive to wireless terminal 200 feedback (e.g., CQI regardingthe downlink channel). For rank 1 transmissions, channel encoder 403 maygenerate a single stream of codewords CW1 responsive to the stream ofdata blocks B1 using only channel encoder CE1. For rank 2 transmissions,channel encoder 403 may generate two streams of codewords CW1 and CW2responsive to respective streams of data blocks B1 and B2 using channelencoder CE1 and channel encoder CE2. For rank 3 transmissions, channelencoder 403 may generate three streams of codewords CW1, CW2, and CW3responsive to respective streams of data blocks B1, B2, and B3 usingchannel encoders CM, CE2, and CE3. For rank 4 transmissions, channelencoder 403 may generate four streams of codewords CW1, CW2, CW3, andCW4 responsive to respective streams of data blocks B1, B2, B3, and B4using channel encoders CE1, CE2, CE3, and CE4. Channel encoder 403 mayapply code rates responsive to input from adaptive controller 415determined based on CQI feedback from wireless terminal 200.

According to some embodiments, the interleavers/modulators (i.e., IM1,IM2, IM3, and/or IM4) and/or the channel encoders (i.e., CE1, CE2, CE3,and/or CE4) may apply different modulation and/or coding characteristics(e.g., different modulation orders and/or coding rates) during rank 2,rank 3, and/or rank 4 transmissions to generate respective (differentlycoded) codewords including data to be transmitted during a same TFRE.For example, wireless terminal feedback for only two modulation and/orcoding characteristics may be supported to reduce signaling overhead.For rank one transmissions, modulation and coding characteristics may bereceived for and applied to channel encoder CE1 andinterleaver/modulator IM1. For rank two transmissions, first modulationand coding characteristics may be received for and applied to channelencoder CE1 and interleaver/modulator IM1, and second modulation andcoding characteristics may be received for and applied to channelencoder CE1 and interleaver/modulator IM2. For rank three transmissions,first modulation and coding characteristics may be received for andapplied to channel encoder CE1 and interleaver/modulator IM1, and secondmodulation and coding characteristics may be received for and applied tochannel encoders CE2 and CE3 and interleavers/modulators IM2 and IM3.For rank four transmissions, first modulation and coding characteristicsmay be received for and applied to channel encoders CE1 and CE4 andinterleavers/modulators IM1 and IM4, and second modulation and codingcharacteristics may be received for and applied to channel encoders CE2and CE3 and interleavers/modulators IM2 and IM3.

Modulator 405 (including interleaver/modulators IM1, IM2, IM3, and IM4)may interleave and modulate the stream/streams of codewords CW1, CW2,CW3, and/or CW4 generated by channel encoder 403 to provide respectivestreams of unmapped symbol blocks D1 (including unmapped symbol blocksd⁽¹⁾-1, d⁽¹⁾-2, d⁽¹⁾-3, etc.), D2 (including unmapped symbol blocksd⁽²⁾-1, d⁽²⁾-2, d⁽²⁾-3, etc.), D3 (including unmapped symbol blocksd⁽³⁾-1, d⁽³⁾-2, d⁽³⁾-3, etc.), and D4 (including unmapped symbol blocksd⁽⁴⁾-1, d⁽⁴⁾-2, d⁽⁴⁾-3, etc.). For rank 1 transmissions (providing only1 MIMO layer/stream), modulator 405 may generate a single stream ofunmapped symbol blocks D1 responsive to the stream of codewords CW1using only interleaver/modulator IM1. For rank 2 transmissions,modulator 405 may generate two streams of unmapped symbol blocks D1 andD2 responsive to respective streams of codewords CW1 and CW2 usinginterleaver/modulators IM1 and IM2. For rank 3 transmissions, modulator405 may generate three streams of unmapped symbol blocks D1, D2, and D3responsive to respective streams of codewords CW1, CW2, and CW3 usinginterleaver/modulators IM1, IM2, and IM3. For rank 4 transmissions,modulator 405 may generate four streams of unmapped symbol blocks D1,D2, D3, and D4 responsive to respective streams of codewords CW1, CW2,CW3, and CW4 using interleaver/modulators IM1, IM2, IM3, and IM4.Modulator 405 may apply modulation orders responsive to input fromadaptive controller 415 determined based on CQI feedback from wirelessterminal 200.

In addition, each interleaver/modulator IM1, IM2, IM3, and/or IM4 mayinterleave data of two or more codewords of a stream so that two or moreconsecutive unmapped symbol blocks of a respective stream includesymbols representing data of the two or more consecutive codewords. Forexample, data of consecutive codewords cw1-1 and cw1-2 of codewordstream CW1 may be interleaved and modulated to provide consecutiveunmapped symbol blocks d⁽¹⁾-1 and d⁽¹⁾-2 of stream D1. Similarly, dataof consecutive codewords cw2-1 and cw2-2 of codeword stream CW2 may beinterleaved and modulated to provide consecutive unmapped symbol blocksd⁽²⁾-1 and d⁽²⁾-2 of stream D2.

Symbols of streams of unmapped symbol blocks D1, D2, D3, and D4 may bemapped to respective streams of mapped symbol blocks X1, X2, X3, and X4(for respective MIMO transmission layers). For rank 1 transmissions,layer mapper 407 may map symbols of unmapped symbol blocks d⁽¹⁾ (fromstream D1) directly to mapped symbol blocks x⁽¹⁾ of stream X1. For rank2 transmissions, layer mapper 407 may map symbols of unmapped symbolblocks d⁽¹⁾ (from stream D1) directly to mapped symbol blocks x⁽¹⁾ ofstream X1, and layer mapper 407 may map symbols of unmapped symbolblocks d⁽²⁾ (from stream D2) directly to mapped symbol blocks x⁽²⁾ ofstream X2. For rank 3 transmissions, layer mapper 407 may map symbols ofunmapped symbol blocks d⁽¹⁾ (from stream D1) directly to mapped symbolblocks x⁽¹⁾ of stream X1, layer mapper 407 may map symbols of unmappedsymbol blocks d⁽²⁾ (from stream D2) directly to mapped symbol blocksx⁽²⁾ of stream X2, and layer mapper 407 may map symbols of unmappedsymbol blocks d⁽³⁾ (from stream D3) directly to mapped symbol blocksx⁽³⁾ of stream X3. For rank 4 transmissions, layer mapper 407 may mapsymbols of unmapped symbol blocks d⁽¹⁾ (from stream D1) directly tomapped symbol blocks x⁽¹⁾ of stream X1, layer mapper 407 may map symbolsof unmapped symbol blocks d⁽²⁾ (from stream D2) directly to mappedsymbol blocks x⁽²⁾ of stream X2, layer mapper 407 may map symbols ofunmapped symbol blocks d⁽³⁾ (from stream D3) directly to mapped symbolblocks x⁽³⁾of stream X3, and layer mapper 407 may map symbols ofunmapped symbol blocks d⁽⁴⁾ (from stream D4) directly to mapped symbolblocks x⁽⁴⁾ of stream X4.

Spreader/scrambler 409 may include four spreader/scramblers SS1, SS2,SS3, and SS4, and for each mapped symbol stream provided by layer mapper407, spreader/scrambler 409 may generate a respective stream of spreadsymbol blocks Y1, Y2, Y3, and Y4 (e.g., using a Walsh code). Layerprecoder 411 may apply a MIMO precoding vector (e.g., by applyingprecoding weights) of the appropriate rank (based on wireless terminalfeedback as interpreted by adaptive controller 415) to the streams ofspread symbol blocks for transmission through transceiver 109 andantennas Ant-1, Ant-2, Ant-3, and Ant-4 of antenna array 117.

In embodiments of FIG. 3, base station processor 101 may support 4 layerMIMO transmissions with four channel encoders CE1, CE2, CE3, and CE4generating respective codeword streams CW1, CW2, CW3, and CW4. Usingfeedback from wireless terminal 200 (indicated by “feedback channel”),adaptive controller 415 may choose transport block length, modulationorder, and coding rate (used by transport block generator 401, encoder403, and/or modulator 405). Adaptive controller 415 may also identifyprecoding vectors (defining precoding weight information) used by layerprecoder 411. Because feedback for only two modulation/coding schemesmay be supported, a same modulation order and/or a same code rate may beapplied to two transmission layers for rank 3 and rank 4 transmissions.For rank 1 transmissions, wireless terminal 200 may provide CQIincluding only one modulation order and only one code rate that areapplied to the stream of codewords CW1 that are modulated and mappeddirectly to transmission layer X1. For rank 2 transmissions, wirelessterminal 200 may provide CQI including a first modulation order and afirst code rate that are applied to the stream of codewords CW1 that aremodulated and mapped directly to transmission layer X1, and a secondmodulation order and a second code rate that are applied to the streamof codewords CW2 that are modulated and mapped directly to transmissionlayer X2. For rank 3 transmissions, wireless terminal 200 may provideCQI including a first modulation order and a first code rate that areapplied to the stream of codewords CW1 that are modulated and mappeddirectly to transmission layer X1, and a second modulation order and asecond code rate that are applied to second and third streams ofcodewords CW2 and CW3 that are modulated and mapped to transmissionlayers X2 and X3. For rank 4 transmissions, wireless terminal 200 mayprovide CQI including a first modulation order and a first code ratethat are applied to the first and fourth streams of codewords CW1 andCW4 that are modulated and mapped to transmission layers X1 and X4, anda second modulation order and a second code rate that are applied tosecond and third streams of codewords CW2 and CW3 that are modulated andmapped to transmission layers X2 and X3. For rank 3 and rank 4transmissions, a same modulation order and a same code rate (alsoreferred to as modulation/coding scheme) may map to more than onetransmission layer.

Based on the rank chosen by adaptive controller 415, transport datablocks may be passed to encoder 403, and encoder outputs may beinterleaved and modulated using modulator 405. Outputs of modulator 405may be mapped to space time layers using layer mapper 407. The symbolstream(s) generated by layer mapper 407 may be spread and scrambledusing spreader/scrambler 409, and layer precoder 411 may precode outputsof spreader/scrambler 409, with precoder outputs being passed throughtransceiver 109 and antenna array 117 (including Antennas Ant-1, Ant-2,Ant-3, and Ant-4).

At wireless terminal 200, operations of processor 201 may mirroroperations of base station processor 101 when receiving the MIMOdownlink communications transmitted by the base station. Moreparticularly, elements/functionalities of wireless terminal processor201 are illustrated in FIG. 4 mirroring elements/functionalities of basestation processor 101 discussed above with reference to FIG. 3.

Radio signals may be received through MIMO antenna elements of MIMOantenna array 217 and transceiver 209, and the radio signals may bedecoded by layer decoder 601 using a MIMO decoding vector to generate aplurality of MIMO decoded symbol layers X1′, X2′, X3′, and/or X4′depending on MIMO rank used for transmission/reception. Layer Decoder601 may use a decoding vector corresponding to the precoding vector usedby base station 100. Layer decoder 601 may generate a single decodedsymbol layer X1′ for rank 1 reception, layer decoder 601 may generatetwo decoded symbol layers X1′ and X2′ for rank 2 reception, layerdecoder 601 may generate three decoded symbol layers X1′, X2′, and X3′for rank 3 reception, and layer decoder 601 may generate four decodedsymbol layers X1′, X2′, X3′, and X4′ for rank 4 transmission. Layerdecoder 601 may thus perform a converse of operations performed by layerprecoder 411 and spreader/scrambler 409 of base station 100. Layerdecoder 601 may perform functionalities of a MIMO detector(corresponding to a converse of layer precoder 411) and ofdispreading/descrambling blocks for each data stream/layer(corresponding to a converse of spreader/scrambler 409). Layer demapper603 may function as a converse of layer mapper 407 to demap decodedsymbol layers X1′, X2′, X3′, and/or X4′ directly to respective unmappedsymbol layers D1′, D2′, D3′, and D4′ according to the transmission rank.

For rank one reception, layer demapper 603 may demap symbols of decodedsymbol layer X1′ blocks x^((1)′)-j directly to symbols of unmappedsymbol layer D1′ blocks d^((1)′)-j, demodulator/deinterleaver DM-1 maydemodulate/deinterleave unmapped symbol layer blocks d^((1)′)-j toprovide codewords cw1′-j of codeword stream CW1′, and channel decoderCD1 may decode codewords cw1′-j of codeword stream CW1′ to providetransport blocks b1′-j of stream B1′. Transport block generator 607 maythen pass transport blocks b1′-j of stream B1′ as a data stream. Duringrank one reception, demodulators/deinterleavers DM2, DM3, and DM4 andchannel decoder CD2, CD3, and CD4 may be unused.

For rank two reception, layer decoder 601 may generate decoded symbollayers X1′ and X2′. Layer demapper 603 may demap symbols of decodedsymbol layer X1′ blocks x^((1)′)-j directly to symbols of unmappedsymbol layer D1′ blocks d^((1)′)-j, and layer demapper 603 may demapsymbols of decoded symbol layer X2′ blocks x^((2)′)-j directly tosymbols of unmapped symbol layer D2′ blocks d^((2)′)j.Demodulator/deinterleaver DM-1 may demodulate/deinterleave unmappedsymbol layer blocks d^((1)′)-j to provide codewords cw1-j of codewordstream CW1′, and demodulator/deinterleaver DM-2 maydemodulate/deinterleave unmapped symbol layer blocks d^((2)′)-j toprovide codewords cw2′-j of codeword stream CW2′. Channel decoder CD1may decode codewords cw1-j of codeword stream CW1′ to provide transportblocks b1′-j of stream B1′, and channel decoder CD2 may decode codewordscw 2′-j of codeword stream CW2′ to provide transport blocks b2′-j ofstream B 2′. Transport block generator 607 may then combine transportblocks b1′-j and b2′-j of streams B1′ and B2′ as a data stream. Duringrank two reception, demodulators/deinterleavers DM3 and DM4 and channeldecoder CD3 and CD4 may be unused.

For rank three reception, layer decoder 601 may generate decoded symbollayers X1′, X2′, and X3′. Layer demapper 603 may demap symbols ofdecoded symbol layer X1′ blocks x^((1)′)-j directly to symbols ofunmapped symbol layer D1′ blocks d^((1)′)-j, layer demapper 603 maydemap symbols of decoded symbol layer X2′ blocks x^((2)′)-j directly tosymbols of unmapped symbol layer D2′ blocks d^((2)′)j, and layerdemapper 603 may demap symbols of decoded symbol layer X3′ blocksx^((3)′)-j directly to symbols of unmapped symbol layer D3′ blocksd^((3)′)-j. Demodulator/deinterleaver DM-1 may demodulate/deinterleaveunmapped symbol layer blocks d^((1)′)-j to provide codewords cw1'-j ofcodeword stream CW1′, demodulator/deinterleaver DM-2 maydemodulate/deinterleave unmapped symbol layer blocks d^((2)′)-j toprovide codewords cw2′-j of codeword stream CW2′, anddemodulator/deinterleaver DM-3 may demodulate/deinterleave unmappedsymbol layer blocks d^((3)′)-j to provide codewords cw3′-j of codewordstream CW3′. Channel decoder CD1 may decode codewords cw1′-j of codewordstream CW1′ to provide transport blocks b1′-j of stream B1′, channeldecoder CD2 may decode codewords cw2′-j of codeword stream CW2′ toprovide transport blocks b2′-j of stream B2′, and channel decoder CD3may decode codewords cw3′-j of codeword stream CW3′ to provide transportblocks b3′-j of stream B3′. Transport block generator 607 may thencombine transport blocks b1′-j, b2′-j, and b3′-j of streams B1′, B2′,and B3′ as a data stream.

For rank four reception, layer decoder 601 may generate decoded symbollayers X1′, X2′, X3′, X4′. Layer demapper 603 may demap symbols ofdecoded symbol layer X1′ blocks x^((1)′)-j to symbols of unmapped symbollayer D1′ blocks d^((1)′)-j, layer demapper 603 may demap symbols ofdecoded symbol layer X2′ blocks x^((2)′)-j to symbols of unmapped symbollayer D2′ blocks d^((2)′)-j, layer demapper 603 may demap symbols ofdecoded symbol layer X3′ blocks x^((3)′)-j to symbols of unmapped symbollayer D3′ blocks d^((3)′)-j, and layer demapper 603 may demap symbols ofdecoded symbol layer X4′ blocks x^((4)′)-j to symbols of unmapped symbollayer D4′ blocks d^((4)′)-j. Demodulator/deinterleaver DM-1 maydemodulate/deinterleave unmapped symbol layer blocks d^((1)′)-j toprovide codewords cw1′-j of codeword stream CW1′,demodulator/deinterleaver DM-2 may demodulate/deinterleave unmappedsymbol layer blocks d^((2)′)-j to provide codewords cw2′-j of codewordstream CW2′, demodulator/deinterleaver DM-3 may demodulate/deinterleaveunmapped symbol layer blocks d^((3)′)-j to provide codewords cw3′-j ofcodeword stream CW3′, and demodulator/deinterleaver DM-4 maydemodulate/deinterleave unmapped symbol layer blocks d^((4)′)-j toprovide codewords cw4′-j of codeword stream CW4′. Channel decoder CD1may decode codewords cw1′-j of codeword stream CW1′ to provide transportblocks b1′-j of stream B1′, channel decoder CD2 may decode codewordscw2′-j of codeword stream CW2′ to provide transport blocks b2′-j ofstream B2′, channel decoder CD3 may decode codewords cw3′-j of codewordstream CW3′ to provide transport blocks b3′-j of stream B3′, and channeldecoder CD4 may decode codewords cw4′-j of codeword stream CW4′ toprovide transport blocks b4′-j of stream B4′. Transport block generator607 may then combine transport blocks b1′-j, b2′-j, b 3′-j, and b 4′-jof streams B1′, B2′, B3′, and B4′ as a data stream.

FIG. 5 is a flow chart illustrating operations of wireless terminal 200(also referred to as user equipment node or user equipment 200)according to some embodiments of the present invention. At block 1101,processor 201 may select a multiple-input-multiple-output, MIMO, rankand a MIMO precoding entity from a codebook of MIMO precoding entitiesfor a downlink communication from the base station (100) to the userequipment. According to some embodiments of the present invention,wireless terminal 200 and base station 200 may support up to four layerMIMO downlink reception using a precoder codebook including 16 precodingentities (also referred to as precoding vectors) for each rank/layer fora total of 64 precoding entities. At block 1103, processor 201 mayselect a modulation/coding scheme to be mapped to first and second MIMOlayers of the downlink communication using the MIMO precoding entityselected from the precoder codebook. At block 1105, processor 201 maythen communicate channel quality information identifying the MIMOprecoding entity and the modulation/coding scheme from the wirelessterminal 200 to the base station 100. More particularly, processor 201may communicate the channel quality information by transmitting thechannel quality information through transceiver 209 and antenna array217 to base station 100.

If processor 201 selects MIMO rank 3 transmission, the modulation/codingscheme may be mapped to channel encoders CE2 and CE3 and/or tointerleaver/modulators IM2 and IM3, and another modulation/coding schememay be selected using the MIMO precoding entity and mapped to channelencoder CE1 and/or to interleaver/modulator IM1. If processor 201selects MIMO rank 4 transmission, the modulation/coding scheme may bemapped to channel encoders CE2 and CE3 and/or to interleaver/modulatorsIM2 and IM3, and another modulation/coding scheme may be selected usingthe MIMO precoding entity and mapped to channel encoders CE1 and CE4and/or to interleavers/modulators IM1 and IM4. Accordingly, the channelquality information may identifying the MIMO precoding entity and bothmodulation/coding schemes.

FIG. 6 is a flow chart illustrating operations of wireless terminal 200according to some other embodiments of the present invention. Moreparticularly, operations of selecting a MIMO precoding vector of block1101 of FIG. 5 may be performed according to operations of blocks 1201to 1207 of FIG. 6, and operations of selecting a modulation/codingscheme mapped to two MIMO layers of block 1103 of FIG. 5 may beperformed according to operations of blocks 1208 to 1219 of FIG. 6.

At block 1201, processor 201 may provide an estimate of the downlinkchannel 300 responsive to pilot signals received from the base station100. The pilot signals may be received at processor 201 from basestation 100 through antenna array 217 and transceiver 209 and processedto provide estimates of the downlink channel (e.g., to provide channelcoefficients). As discussed above, wireless terminal 200 may supportreception of up to 4 downlink transmission layers, and the precodingcodebook may include 64 precoding entities, with 16 precoding entitiesprovided for each of the 4 downlink transmission layers/ranks. In thetables of FIGS. 7A to 7D, the precoding entities/indices are identifiedas P_(i,j), where i indicates the rank and j indicates the index withinthe rank. At block 1203, processor 201 may use the estimate of thedownlink channel to estimate signal strengths (e.g., signal to noiseratios or SNRs) S_(i,k,j) for each applicable layer of each precodingentity P_(i,j), where i indicates the rank, k indicates the layer, and jindicates the index within the rank. As shown in FIG. 7A, one signalstrength is estimated for each rank 1 precoding vector because rank 1supports 1 MIMO transmission/reception layer. As shown in FIG. 7B, twosignal strengths are estimated for each rank 2 precoding vector becauserank 2 supports 2 MIMO transmission/reception layers. As shown in FIG.7C, three signal strengths are estimated for each rank 3 precodingvector because rank 3 supports 3 MIMO transmission/reception layers. Asshown in FIG. 7D, four signal strengths are estimated for each rank 4precoding vector because rank 4 supports 4 MIMO transmission/receptionlayers.

At block 1205, processor 201 may estimate capacities for the precodingentities of the codebook using the signal strengths of FIGS. 7A to 7D toprovide the capacities C_(i,j) of FIGS. 8A to 8D corresponding to therespective precoding entities P_(i,j), where i indicates the rank, and jindicates the index within the rank. More particularly, a capacity foreach layer of each precoding entity may be calculated using therespective signal strength (e.g., SNR) from the tables of FIGS. 7A to 7Dwhere the capacity for each layer may be calculated as:

C=log2(1+SNR),

and the capacity of a precoding entity may be calculated by summing thecapacities of its respective layers. Accordingly, the capacity C_(1,j)of each rank one precoding entity P_(i,j) may be calculated as:

C _(1,j)=log2(1+S _(1,1,j)).

The capacity C_(2,j) of each rank two precoding entity P_(2,j) may becalculated as:

C _(2,j)=log2(1+S _(2,1,j))+log2(1+S _(2,2,j)).

The capacity C_(3,j) of each rank two precoding entity P_(3,j) may becalculated as:

C _(3,j)=log2(1+S _(3,1,j))+log2(1+S _(3,2,j))+log2(1+S _(3,3,j)).

The capacity C_(4,j) of each rank two precoding entity P_(4,j) may becalculated as:

C _(4,j)=log2(1+S _(4,1,j))+log2(1+S _(4,2,j))+log2(1+S_(4,3,j))+log2(1+S _(4,4,j)).

At block 1207, processor 201 may select the precoding rank and precodingentity based on the capacities of FIGS. 8A to 8D. For example, processor201 may select the rank and precoding entity corresponding to thehighest/greatest capacity C_(i,j). Stated in other words, processor 201may select the rank and precoding entity to increase/maximize capacityC_(i,j).

Depending on the rank at block 1208, processor 201 may select amodulation/coding scheme according to one of blocks 1209, 1211, 1215,and/or 1219. For rank 1 at block 1209, one modulation/coding scheme MCS1is selected mapping to only one transmission/reception layer (e.g.,including channel encoder CE1, interleaver/modulator IM1,demodulator/deinterleaver DM1, and/or channel decoder CD1), andprocessor 201 may select modulation/coding scheme MCS1 using therespective layer 1 signal strength S_(1,1,j) corresponding to theselected precoding entity P_(1,j). As shown in FIG. 9, for rank 1, afirst modulation/coding scheme MCS1 is chosen as a function ofS_(1,1,j).

For rank 2 at block 1211, first and second modulation/coding schemesMCS1 and MCS2 are selected. The first modulation/coding scheme MCS1 mapsto a first transmission/reception layer (e.g., including channel encoderCE1, interleaver/modulator IM1, demodulator/deinterleaver DM1, and/orchannel decoder CD1), and processor 201 may select modulation/codingscheme MCS1 using the respective layer 1 signal strength S_(2,1,j)corresponding to the selected precoding entity P_(2,j). The secondmodulation/coding scheme MCS2 maps to a second transmission/receptionlayer (e.g., including channel encoder CE2, interleaver/modulator IM2,demodulator/deinterleaver DM2, and/or channel decoder CD2), andprocessor 201 may select modulation/coding scheme MCS2 using therespective layer 2 signal strength S_(2,2,j) corresponding to theselected precoding entity P_(2,j). As shown in FIG. 9, for rank 2, afirst modulation/coding scheme MCS1 is chosen as a function ofS_(2,1,j), and a second modulation/coding scheme MCS2 is chosen as afunction of S_(2,2,j).

For rank 3 at block 1215, first and second modulation/coding schemesMCS1 and MCS2 are selected. The first modulation/coding scheme MCS1 mapsto a first transmission/reception layer (e.g., including channel encoderCE1, interleaver/modulator IM1, demodulator/deinterleaver DM1, and/orchannel decoder CD1), and processor 201 may select modulation/codingscheme MCS1 using the respective layer 1 signal strength S_(3,1,j)corresponding to the selected precoding entity P_(3,j). The secondmodulation/coding scheme MCS2 maps to second and thirdtransmission/reception layer (e.g., including channel encoders CE2/CE3,interleavers/modulators IM2/IM3, demodulators/deinterleavers DM2/DM3,and/or channel decoders CD2/CD3), and processor 201 may selectmodulation/coding scheme MCS2 using (e.g., as a function of) therespective layer 2 and/or 3 signal strengths S_(3,2,j) and/or S_(3,3,j)corresponding to the selected precoding entity P_(3,j), As shown in FIG.9, for rank 3, a first modulation/coding scheme MCS1 is chosen as afunction of and a second modulation/coding scheme MCS2 is chosen as afunction of S_(3,2,j) and/or S_(3,3,j). By way of example, the secondmodulation/coding scheme MCS2 may be selected responsive to (e.g., as afunction of): an average of S_(3,2,j) and/or S_(3,3,j) corresponding tothe selected precoding entity P_(3,j); a maximum of S_(3,2,j) and/orS_(3,3,j) corresponding to the selected precoding entity P_(3,j); and/ora minimum of S_(3,2,j) and/or S_(3,3,j) corresponding to the selectedprecoding entity P_(3,j).

The MIMO rank and precoding entity selected at block 1207 and themodulation/coding scheme(s) selected at block 1209/1211/1215/1219 maythen be included in channel quality information CQI that is transmittedto base station 100 at block 1105.

FIG. 10 is a flow chart illustrating operations of wireless terminal 200according to some other embodiments of the present invention. Moreparticularly, operations of selecting a MIMO precoding vector of block1101 of FIG. 5 may be performed according to operations of blocks 1301to 1311 of FIG. 10, and operations of selecting a modulation/codingscheme mapped to two MIMO layers of block 1103 of FIG. 5 may beperformed according to operations of block 1315 of FIG. 10.

At block 1301, processor 201 may provide an estimate of the downlinkchannel 300 responsive to pilot signals received from the base station100. The pilot signals may be received at processor 201 from basestation 100 through antenna array 217 and transceiver 209 and processedto provide estimates of the downlink channel (e.g., to provide channelcoefficients). As discussed above, wireless terminal 200 may supportreception of up to 4 downlink transmission layers, and the precodingcodebook may include 64 precoding entities, with 16 precoding entitiesprovided for each of the 4 downlink transmission layers/ranks. In thetables of FIGS. 7A to 7D, the precoding entities/indices are identifiedas P_(i,j) where i indicates the rank and j indicates the index withinthe rank. At block 1303, processor 201 may use the estimate of thedownlink channel to estimate signal strengths (e.g., signal to noiseratios or SNRs) S_(i,k,j) for each applicable layer of each precodingentity P_(i,j), where i indicates the rank, k indicates the layer , andj indicates the index within the rank.

At block 1305, processor 101 may select a respective modulation/codingscheme M_(i,k,j) for each of the relevant layers k of each of the MIMOprecoding entities P_(i,j) of the codebook as shown in FIGS. 13A to 13Dresponsive to the respective signal strengths S_(i,k,j) of FIGS. 7A to7D (e.g., using lookup tables). For each rank 1 precoding entityP_(i,j), one modulation/coding scheme M_(1,1,j) is selected responsiveto the respective signal strength S_(i,k,j). For each rank 2 precodingentity P_(2,j), two modulation/coding schemes M_(2,1,j) and M_(2,2,j)are selected responsive to the respective signal strengths S_(2,1,j) andS_(2,1,k). For each rank 3 precoding entity P_(3,j), threemodulation/coding schemes M_(3,1,j), M_(3,2,j), and M_(3,3,j) areselected responsive to the respective signal strengths S_(3,1,j),S_(3,2,j), and S_(3,3,j). For each rank 4 precoding entity P_(4,j), fourmodulation/coding schemes M_(4,1,j), M_(4,2,j),M_(4,3,j), and M_(4,4,j)are selected responsive to the respective signal strengths S_(4,1,j),S_(4,2,j), S_(4,3,j), and S_(4,4,j).

At block 1307, processor 201 calculates a respective spectral efficiencyE_(i,k,j) (also referred to as a layer efficiency) for each of thelayers k of each of the MIMO precoding entities P_(i,j) of the codebookresponsive to the respective modulation/coding schemes M_(i,k,j) ofFIGS. 13A to 13D. Spectral efficiencies E_(i,k,j) of each of the layersare illustrated in FIGS. 14A to 14D. Each spectral efficiency E_(i,k,j)may be calculated as:

E=log2(M)R,

where M is the number of constellation points in the selectedmodulation/coding scheme and R is the code rate of the selectedmodulation/coding scheme.

At block 1309, processor 201 may provide a respective precoding entityspectral efficiency SE_(i,j) for each of the MIMO precoding entities ofthe codebook responsive to the layer efficiencies of the respective MIMOprecoding entities as shown in FIGS. 15A to 15D. Each precoding spectralefficiency SE_(i,j) may be calculated as discussed below with respect toFIG. 11A or as discussed below with respect to FIG. 11B.

As shown in FIG. 11A, a maximum spectral efficiency may be selected fortwo layers sharing a modulation/coding scheme for ranks 3 and 4. Forrank one precoding entities P_(1,j) at block 1401, processor 201 maycalculate precoding entity spectral efficiencies SE_(1,j) as a functionof the respective layer 1 efficiency E_(1,1,j) as follows:

SE _(1,j) =E _(1,1,j)=log2(M _(1,1,j))R _(1,1,j).

For rank two precoding entities P_(2,j) at block 1403, processor 201 maycalculate precoding entity spectral efficiencies SE_(2,j) as a functionof the respective layer 1 and 2 efficiencies E_(2,1,j) and E_(2,2,j) asfollows:

SE _(2j) =E _(2,1,j) +E _(2,2,j)=log2(M _(2,1,j))R _(2,1j)+log2(M_(2,2,j))R _(2,2,j).

For rank three precoding entities P_(,3,j) at block 1405, processor 201may calculate precoding entity spectral efficiencies SE_(3,j) as afunction of the respective layer 1, 2, and 3 efficiencies E_(3,1,j),E_(3,2,j), and E_(3,3,j) as follows:

$\begin{matrix}{{SE}_{3,j} = {E_{3,1,j} + {2*{{Max}\left( {E_{3,2,j},E_{3,3,j}} \right)}}}} \\{= {{\log \; 2\left( M_{3,1,j} \right)R_{3,1,j}} +}} \\{{2*{{{Max}\left\lbrack {{\log \; 2\left( M_{3,2,j} \right)R_{3,2,j}},{\log \; 2\left( M_{3,3,j} \right)R_{3,3,j}}} \right\rbrack}.}}}\end{matrix}$

For rank four precoding entities P_(4,j) at block 1407, processor 201may calculate precoding entity spectral efficiencies SE_(4,j) as afunction of the respective layer 1, 2, 3, and 4 efficiencies E_(4,1,j),E_(4,2,j), E_(4,3,j), and E_(4,4,j) as follows:

$\begin{matrix}{{SE}_{3,j} = {{2*{{Max}\left( {E_{4,1,j},E_{4,{4j}}} \right)}} + {2*{{Max}\left( {E_{4,2,j},E_{4,3,j}} \right)}}}} \\{= {{2*{{Max}\left\lbrack {{\log \; 2\left( M_{4,1,j} \right)R_{4,1,j}},{\log \; 2\left( M_{4,4,j} \right)R_{4,4,j}}} \right\rbrack}} +}} \\{{2*{{{Max}\left\lbrack {{\log \; 2\left( M_{4,2,j} \right)R_{4,2,j}},{\log \; 2\left( M_{4,3,j} \right)R_{4,3,j}}} \right\rbrack}.}}}\end{matrix}$

As shown in FIG. 11B, a minimum spectral efficiency may be selected fortwo layers sharing a modulation/coding scheme for ranks 3 and 4. Forrank one precoding entities P_(1,j) at block 1501, processor 201 maycalculate precoding entity spectral efficiencies SE_(1,j) as a functionof the respective layer 1 efficiency E_(1,1,j) as follows:

SE _(1,j) =E _(1,1,j)=log(M _(1,1,j))R _(1,1,j).

For rank two precoding entities P_(2,j) at block 1503, processor 201 maycalculate precoding entity spectral efficiencies SE_(2,j) as a functionof the respective layer 1 and 2 efficiencies E_(2,1,j) and E_(2,2,j) asfollows:

SE _(2,j) =E _(2,1,j) +E _(2,2,j)=log2(M _(2,1,j))R _(2,1,j)+log2(M_(2,2,j))R _(2,2,j).

For rank three precoding entities P_(3,j) at block 1505, processor 201may calculate precoding entity spectral efficiencies SE_(3,j) as afunction of the respective layer 1, 2, and 3 efficiencies E_(3,1,j),E_(3,2,j), and E_(3,3,j) as follows:

$\begin{matrix}{{SE}_{3,j} = {E_{3,1,j} + {2*{{Min}\left( {E_{3,2,j},E_{3,3,j}} \right)}}}} \\{= {{\log \; 2\left( M_{3,1,j} \right)R_{3,1,j}} +}} \\{{2*{{{Min}\left\lbrack {{\log \; 2\left( M_{3,2,j} \right)R_{3,2,j}},{\log \; 2\left( M_{3,3,j} \right)R_{3,3,j}}} \right\rbrack}.}}}\end{matrix}$

For rank four precoding entities P_(4,j) at block 1507, processor 201may calculate precoding entity spectral efficiencies SE_(4,j) as afunction of the respective layer 1, 2, 3, and 4 efficiencies E_(4,1,j),E_(4,3,j), E_(4,3,j), and E_(4,4,j) as follows:

$\begin{matrix}{{SE}_{3,j} = {{2*{{Min}\left( {E_{4,1,j},E_{4,4,j}} \right)}} + {2*{{Min}\left( {E_{4,2,j},E_{4,3,j}} \right)}}}} \\{= {{2*{{Min}\left\lbrack {{\log \; 2\left( M_{4,1,j} \right)R_{4,1,j}},{\log \; 2\left( M_{4,4,j} \right)R_{4,4,j}}} \right\rbrack}} +}} \\{{2*{{{Min}\left\lbrack {{\log \; 2\left( M_{4,2,j} \right)R_{4,2,j}},{\log \; 2\left( M_{4,3,j} \right)R_{4,3,j}}} \right\rbrack}.}}}\end{matrix}$

At block 1311, processor 201 may select a MIMO rank and precoding entityresponsive to the combined efficiencies SE_(i,j) provided at block 1309and FIGS. 15A to 15D. More particularly, processor 201 may select theMIMO rank and precoding entity P_(i,j) corresponding to the highestcombined efficiency SE_(i,j), calculated at block 1309. At block 1315,processor 201 may select one modulation/coding scheme MCS1 for rank 1 ortwo modulation/coding schemes MCS1 and MCS2 for rank 2, 3, and 4corresponding to the selected MIMO rank and precoding entity. Ifoperations of FIG. 11A are used to provide the combined efficiencies atblock 1309, operations of FIG. 12A may be used to select themodulation/coding scheme(s) at block 1315. If operations of FIG. 11B areused to provide the combined efficiencies at block 1309, operations ofFIG. 12B may be used to select the modulation/coding scheme(s) at block1315.

In FIG. 12A depending on the rank, processor 201 may select themodulation/coding scheme(s) using operations of blocks 1603, 1605, 1607,or 1609. For rank 1 precoding entities P_(1,j) at block 1603, processor101 may select a modulation/coding scheme MCS1=M_(1,1,j) from FIG. 13A(corresponding to the selected precoding entity P_(i,j)) that is mappedto one MIMO transmission/reception layer (e.g., including CE1, IM1, DM1,and/or CD1). For rank 2 precoding entities P_(2,j) at block 1605,processor 101 may select a first modulation/coding scheme MCS1=M_(2,1,j)from FIG. 13B (corresponding to the selected precoding entity P_(2,j))that is mapped to a first MIMO transmission/reception layer (e.g.,including CE1, IM1, DM1, and/or CD1), and a second modulation/codingscheme MCS2=M_(2,2,j) from FIG. 13B (corresponding to the selectedprecoding entity P_(2,j)) that is mapped to a second MIMOtransmission/reception layer (e.g., including CE2, IM2, DM2, and/orCD2).

For rank 3 precoding entities P_(3,j) at block 1607, processor 101 mayselect a first modulation/coding scheme MCS1=M_(3,1,j) from FIG. 13B(corresponding to the selected precoding entity P_(3,j)) that is mappedto a first MIMO transmission/reception layer (e.g., including CE1, IM1,DM1, and/or CD1). In addition, processor 101 may select a secondmodulation/coding scheme MCS2 equal to M_(3,2,j) or M_(3,3,j)(corresponding to P_(3,j)) providing higher efficiency as indicated bycorresponding layer efficiencies E_(3,2,j) or E_(3,3,j) from FIG. 14C.Moreover, the second modulation/coding scheme MCS2 for rank 3 may bemapped to second and third MIMO transmission/reception layers (e.g.,including CE2, IM2, DM2, and/or CD2, and/or including CE3, IM3, DM3,and/or CD3).

For rank 4 precoding entities P_(4,j) at block 1609, processor 101 mayselect a first modulation/coding scheme MCS1 equal to M_(4,1,j) orM_(4,4,j) (corresponding to P_(4,j)) providing higher efficiency asindicated by corresponding layer efficiencies E_(4,1,j) or E_(4,4,j)from FIG. 14D. Moreover, the first modulation/coding scheme MCS2 forrank 4 may be mapped to first and fourth MIMO transmission/receptionlayers (e.g., including CE1, IM1, DM1, and/or CD1, and/or including CE4,IM4, DM4, and/or CD4). In addition, processor 101 may select a secondmodulation/coding scheme MCS2 equal to M_(4,2,j) or M_(4,3,j)(corresponding to PO providing higher efficiency as indicated bycorresponding layer efficiencies E_(4,2,j) or E_(4,3,j) from FIG. 14D.Moreover, the second modulation/coding scheme MC2 for rank 4 may bemapped to second and third MIMO transmission/reception layers (e.g.,including CE2, IM2, DM2, and/or CD2, and/or including CE3, IM3, DM3,and/or CD3).

In FIG. 12B depending on the rank, processor 201 may select themodulation/coding scheme(s) using operations of blocks 1703, 1705, 1707,or 1709. For rank 1 precoding entities P_(1,j) at block 1703, processor101 may select a modulation/coding scheme MCS1=M_(1,1,j) from FIG. 13A(corresponding to the selected precoding entity P_(1,j)) that is mappedto one MIMO transmission/reception layer (e.g., including CE1, IM1, DM1,and/or CD1). For rank 2 precoding entities P_(2,j) at block 1705,processor 101 may select a first modulation/coding scheme MCS1=M_(2,1,j)from FIG. 13B (corresponding to the selected precoding entity P_(2,j))that is mapped to a first MIMO transmission/reception layer (e.g.,including CE1, IM1, DM1, and/or CD1), and a second modulation/codingscheme MCS2=M_(2,2,j) from FIG. 13B (corresponding to the selectedprecoding entity P_(2,j)) that is mapped to a second MIMOtransmission/reception layer (e.g., including CE2, IM2, DM2, and/orCD2).

For rank 3 precoding entities P_(3,j) at block 1707, processor 101 mayselect a first modulation/coding scheme MCS1=M_(3,1,j) from FIG. 13B(corresponding to the selected precoding entity P_(3,j)) that is mappedto a first MIMO transmission/reception layer (e.g., including CE1, IM1,DM1, and/or CD1). In addition, processor 101 may select a secondmodulation/coding scheme MCS2 equal to M_(3,2,j) or M_(3,3,j)(corresponding to P_(3,j)) providing lower efficiency as indicated bycorresponding layer efficiencies E_(3,2,j) or E_(3,3,j) from FIG. 14C.Moreover, the second modulation/coding scheme MCS2 for rank 3 may bemapped to second and third MIMO transmission/reception layers (e.g.,including CE2, IM2, DM2, and/or CD2, and/or including CE3, IM3, DM3,and/or CD3).

For rank 4 precoding entities M_(4,j) at block 1709, processor 101 mayselect a first modulation/coding scheme MCS1 equal to M_(4,1,j) orM_(4,4,j) (corresponding to P_(4,j)) providing lower efficiency asindicated by corresponding layer efficiencies E_(4,1,j) or E_(4,4,j)from FIG. 14D. Moreover, the first modulation/coding scheme MCS2 forrank 4 may be mapped to first and fourth MIMO transmission/receptionlayers (e.g., including CE1, IM1, DM1, and/or CD1, and/or including CE4,IM4, DM4, and/or CD4). In addition, processor 101 may select a secondmodulation/coding scheme MCS2 equal to M_(4,2,j) or M_(4,3,j)(corresponding to P_(4,j)) providing lower efficiency as indicated bycorresponding layer efficiencies E_(4,2,j) or E_(4,3,j) from FIG. 14D.Moreover, the second modulation/coding scheme MCS2 for rank 4 may bemapped to second and third MIMO transmission/reception layers (e.g.,including CE2, IM2, DM2, and/or CD2, and/or including CE3, IM3, DM3,and/or CD3).

The MIMO rank and precoding entity selected at block 1311 and themodulation/coding scheme(s) selected at block 1315 may then be includedin channel quality information CQI that is transmitted to base station100 at block 1105.

Various embodiments of the present invention are directed to methods andapparatus that determine channel quality information (CQI) for a 4branch MIMO using fewer codewords for ranks greater than 2. In aconventional approach, one codeword is used for rank 1, two codewordsare used for rank 2, 3 codewords are used for rank 3, and 4 codewordsare used for rank 4. In contrast, in accordance with some embodiments ofthe present invention, one codeword is used for rank 1, while twocodewords are used for ranks 2, 3, and 4. A potential problem can arisewhen only two codewords are used for rank 3 and 4, however this problemmay be overcome/addressed using one or more of the following approachesto map signal to noise ratios (SNRs) for link adaptation.

Alternative embodiments of the base station (e.g., Evolved Node B,eNodeB) of FIG. 3 may support 4 transmit MIMO using 2 codewords (e.g.,eliminating transport blocks TB3 and TB4, channel encoders CE3 and CE4,and interleavers/modulators IM3 and IM4) mapped to four symbol layersX1, X2, X3, and X4 as shown in FIG. 17. eNodeB is an acronym for anEvolved Universal Terrestrial Radio Access Network (E-UTRAN) NodeB. Thenetwork node receives feedback information on a feedback channel 2130from a User Equipment node (UE), and an adaptive controller 2100 usesthe feedback information to choose a transport block length, amodulation order and a coding rate. The adaptive controller 2100 alsogenerates precoding weight information. In this non-limiting embodiment,the feedback information may corresponds to a maximum of 2 codewords.Based on a rank chosen by the adaptive controller 2100, transport blocksof equal size are bundled (for ranks 3 and 4) and passed to a pair ofchannel encoders 2112′, 2112″ and the respective outputs thereof areinterleaved and modulated by a pair of interleaver-modulators 2114′,2114″. Outputs of modulators 2114′, 2114″ are mapped to the space timelayers using layer mapper 2116. In this non-limiting embodiment, thelayers may be mapped according to the table of FIG. 18 where d^(k)(i)denotes the i^(th) symbol at the output of the k^(th) modulator 2114 andx^(i(i) denotes the i) ^(th) symbol at the output of the j^(th) layerand M denotes the maximum number of symbols supported per layer.

In this non-limiting embodiment, for ranks 1 and 2 the layer mapping isone to one. In contrast, for ranks 3 and 4 each codeword is mapped tomore than one layer, such as illustrated in the table of FIG. 18.Following the layer mapping, the resultant symbols are spread andscrambled by a set of spreader and scramblers 2118′- 2118″″. Precodingis applied by a precoder 2120 to the output of the spreader andscramblers 2118′- 2118″″, and the resulting output signal is passed tothe corresponding antenna ports (Ant 1, Ant 2, Ant 3, Ant 4).

The feedback channel 2130 provides channel quality information, such asa modulation and coding scheme that is suitable for use in a nextTransmission Time Interval (TTI). The CQI report can also include rankinformation and a precoding control index (PCI).

One approach to choose these parameters may be provided as follows:

1. A UE computes the channel coefficients by estimating the channel;

2. The Signal to Noise Ration (SNR) is computed for each entity in theprecoding codebook;

3. The capacity of each entity is computed using the following formula:C=log2(1+SNR);

4. A PCI is determined that increases/maximizes capacity; and

5. With the corresponding SNR, link adaptation is performed to choose amodulation and coding scheme that is suitable for this SNR (e.g., usinglookup tables).

For 4×4 MIMO with two codewords, and for ranks 3 and 4, for eachprecoding entity in the codebook, two modulation and coding indices arechosen by a UE from four received SNRs. Two approaches are describedbelow which can be performed by a UE to choose suitable modulation andcoding schemes as well as precoding and rank information for a 4×4 MIMOsystem with two codewords in accordance with various embodiments.

According to some embodiments, FIG. 19 shows a block diagram of amodulation and coding circuit of a UE that is configured to choose amodulation and coding scheme for a 4×4 MIMO system with two codewordsaccording to some embodiments of the present invention. For ranks 1 and2, computing the modulation and coding scheme may be performed accordingto a conventional method. However, for ranks 3 and 4, SNRs may becomputed using SNR Estimator 2200 from the channel coefficient(s) and adefined precoding control index. The computed SNRs may be passed througha pair of decision modules 210′, 210″ and respective link adaptationmodules LAs 220′, 220″ for computation of respective modulation andcoding schemes MCS1, MCS2, which can be communicated to a base stationvia the feedback channel 2130 to control further transmission therefromto the UE.

As shown in FIG. 19, each of the decision modules 2210′, 2210″ mayreceive two SNRs which have been computed (estimated) by the SNREstimator 200. Each decision module may combine the two SNRs to output asingle SNR that is used by a corresponding link adaptation module. Thedecision module can combine the two SNRs into a single SNR byselecting: 1) a minimum of the input SNRs to generate an output SNR; 2)selecting a maximum of the input SNRs to generate an output SNR; 3)averaging the input SNRs to generate an output SNR; or 4) combining theinput SNRs according to another defined algorithm to generate an outputSNR. Each of the link adaptation modules 2220′, 2220″ may use therespective SNR from the corresponding decision module 2210′, 2210″ tochoose a corresponding modulation and coding scheme (MCS1, MCS2) using,for example, a look up table of MCS entries that are referenced usingthe input SNR.

Further embodiments may combine one or more of the operations andmethods of the first approach.

According to some other embodiments, FIG. 20 shows a block diagram of amodulation and coding circuit of a UE that is configured to choose amodulation and coding scheme. SNR Estimator 2300 may use channelcoefficients to compute SNRs for each of the hypothesis (which mayoperate according to the SNR estimator of FIG. 19). SNR estimator 2300may output four SNR estimate values. The link adaptation modules 2310′,2310″, 2310″′, 2310″′may each use a different one of the four SNRs toperform link adaptation to output a modulation and coding scheme. Thelink adaptation modules may operate in a conventional manner to selectthe modulation and coding scheme, such as using the input SNR as apointer within a defined look up table of MCS entries. As shown in FIG.20, each decision module 2320′, 2320″ may combine two of the modulationand coding schemes output by a pair of the link adaptation modules2310′- 2310″, 2310′″- 2310″″ to output a single modulation and codingscheme, which can be communicated to a base station via the feedbackchannel 2130 to control further transmission therefrom to the UE.

Thus, for example, the decision module 2320′ may combine a modulationand coding scheme output by link adaptation modules 2310′ and 2310″ intoa single modulation and coding scheme MCS1, which is communicated to thebase station via the feedback channel 2130. Similarly, the decisionmodule 2320″ may combine a modulation and coding scheme output by linkadaptation modules 2310″′ and 2310″″ into a single modulation and codingscheme MCS2, which is communicated to the base station via the feedbackchannel 2130.

To combine the modulation and coding schemes, the decision modules2320′, 2320″ may each compute the spectral efficiency of different onesof an input pair of the modulation and coding scheme according to thefollowing formula:

SE=log2(M)R,

where M is the number of constellation points in the selectedmodulation, and R is the code rate. The decision modules 2320′, 2320″may also compare the spectral efficiencies computed to output amodulation coding scheme MCS1, MCS2, respectively, that corresponds to:

1. Minimum spectral efficiency; and/or

2. Maximum spectral efficiency.

FIG. 16 is a non-limiting example graph illustrating link levelperformance that may be obtained for a 4×4 MIMO system with 4 codewords(data points indicated with squares) and 2 codewords (data pointsindicated with circles) using various embodiments of the presentinvention. The user throughput in Mbps as a function of geometry factor(Îor/Ioc) in dB for the two approaches is illustrated. Significant gainsmay be obtained using 4×4 MIMO with 4 and 2 codewords as compared to 2×2MIMO. For low geometries, performance with 2 codewords may be almostidentical to that of 4 codewords, because at low geometries, there maybe a relatively high probability that rank is either 1 or 2. For ranks 1and 2, the approaches may have the same layer mapping. For highergeometries, performance with 4 codewords may be slightly better comparedto that of 2 codewords. For example, at a geometry factor equal to 25dB, user throughput gain of 9% may be observed for 4 codeword MIMOcompared to that of 2 codeword MIMO. These computations assume perfectchannel estimation and perfect link adaptation, and by addingimperfections it may be expected that the gains of 4 codeword maydegrade compared to 2 codewords.

Some embodiments are directed to a method in a base station thatcommunicates with a UE. The method may include receiving feedbackinformation on a feedback channel from the UE. Transport blocks areencoded to form codewords which are mapped to space time layers based onranks that are selected responsive to the feedback information. Forranks 1 and 2, each codeword is mapping to one space time layer. Forranks 3 and 4, each codeword is mapped to more than one space timelayer.

In a further embodiment, the mapping of the transport blocks to thespace time layers includes choosing a transport block length, amodulation order and a coding rate in response to the feedbackinformation. In a further embodiment, when the selected rank is 3 or 4,the method further includes bundling the transport blocks, channelencoding the bundled transport blocks to generate the codewords,interleaving and modulating the encoded transport blocks to generateoutput codewords, and mapping the output codewords to the space timelayers.

In a further embodiment, the feedback information corresponds to amaximum of 2 codewords. In a further embodiment, the space time layerscan be mapped to the codewords according to the table of FIG. 18.

In a further embodiment, the feedback channel provides channel qualityinformation for use in a next Transmission Time Interval (TTI). In afurther embodiment, the channel quality information includes amodulation and coding scheme. In a further embodiment, in response to a4×4 MIMO with two codewords and the selected rank being 3 or 4, themethod further comprises choosing two modulation and coding indices fromfour received SNRs for each precoding entity in the codebook.

Another embodiment is directed to a User Equipment node (UE) thatincludes a modulation and coding circuit for a 4×4 MIMO system with twocodewords. When a selected rank is 3 or 4, a SNR estimator computes SNRin response to a channel coefficient(s) and a defined precoding controlindex. The computed SNR is passed through a pair of decision modules andrespective link adaptation modules which compute respective modulationand coding schemes.

In further embodiments, the SNR estimator outputs four SNRs, and each ofthe decision modules combines a different pair of the SNRs to output asingle SNR to a corresponding one of the link adaptation modules for usein computing a modulation and coding scheme.

In further embodiments, each of the decision modules receives at leasttwo SNRs from the SNR estimator, and combines the at least two SNRs intoa single SNR by selecting: 1) a minimum of the input SNRs to generate anoutput SNR; 2) selecting a maximum of the input SNRs to generate anoutput SNR; 3) averaging the input SNRs to generate an output SNR; or 4)combining the input SNRs according to another defined algorithm togenerate an output SNR. Each of the link adaptation modules choose amodulation and coding scheme in response to the SNR output from adifferent one of the decision modules.

Another embodiment is directed to a User Equipment node (UE) thatincludes a modulation and coding circuit that includes a SNR estimatorthat uses channel coefficients to compute the SNR for each of thehypothesis to output SNR values. Link adaptation modules respond todifferent ones of the SNR values to output modulation and codingschemes. Decision modules compute the spectral efficiency of differentpairs of the modulation and coding schemes. In a further embodiment, thedecision modules compute the spectral efficiency according to thefollowing formula:

SE=log2(M) R;

where M is the number of constellation points in the selectedmodulation, and R is the code rate.

In a further embodiment, the SNR estimator outputs four SNR values whichare input to different ones of four of the link adaptation modules. Eachof the link adaptation modules select a modulation and coding schemewhich is output. A pair of decision modules combines two of themodulation and coding schemes output from a different pair of the linkadaptation modules to each output a single modulation and coding scheme.

In a further embodiment, each of the decision modules may compare thespectral efficiencies for each of the modulation and coding schemesreceived from the link adaptation modules to select between themodulation and coding schemes and/or to combine the modulation andcoding schemes into a single modulation coding scheme that correspondsto a minimum spectral efficiency and/or a maximum spectral efficiency ofthe received modulation and coding schemes.

In the above-description of various embodiments of the presentinvention, it is to be understood that the terminology used herein isfor the purpose of describing particular embodiments only and is notintended to be limiting of the invention. Unless otherwise defined, allterms (including technical and scientific terms) used herein have thesame meaning as commonly understood by one of ordinary skill in the artto which this invention belongs. It will be further understood thatterms, such as those defined in commonly used dictionaries, should beinterpreted as having a meaning that is consistent with their meaning inthe context of this specification and the relevant art and will not beinterpreted in an idealized or overly formal sense expressly so definedherein.

When an element is referred to as being “connected”, “coupled”,“responsive”, or variants thereof to another element, it can be directlyconnected, coupled, or responsive to the other element or interveningelements may be present. In contrast, when an element is referred to asbeing “directly connected”, “directly coupled”, “directly responsive”,or variants thereof to another element, there are no interveningelements present. Like numbers refer to like elements throughout.Furthermore, “coupled”, “connected”, “responsive”, or variants thereofas used herein may include wirelessly coupled, connected, or responsive.As used herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. Well-known functions or constructions may not be described indetail for brevity and/or clarity. The term “and/or” includes any andall combinations of one or more of the associated listed items.

As used herein, the terms “comprise”, “comprising”, “comprises”,“include”, “including”, “includes”, “have”, “has”, “having”, or variantsthereof are open-ended, and include one or more stated features,integers, elements, steps, components or functions but does not precludethe presence or addition of one or more other features, integers,elements, steps, components, functions or groups thereof. Furthermore,as used herein, the common abbreviation “e.g.”, which derives from theLatin phrase “exempli gratia,” may be used to introduce or specify ageneral example or examples of a previously mentioned item, and is notintended to be limiting of such item. The common abbreviation “i.e.”,which derives from the Latin phrase “id est,” may be used to specify aparticular item from a more general recitation.

Example embodiments are described herein with reference to blockdiagrams and/or flowchart illustrations of computer-implemented methods,apparatus (systems and/or devices) and/or computer program products. Itis understood that a block of the block diagrams and/or flowchartillustrations, and combinations of blocks in the block diagrams and/orflowchart illustrations, can be implemented by computer programinstructions that are performed by one or more computer circuits. Thesecomputer program instructions may be provided to a processor circuit ofa general purpose computer circuit, special purpose computer circuit,and/or other programmable data processing circuit to produce a machine,such that the instructions, which execute via the processor of thecomputer and/or other programmable data processing apparatus, transformand control transistors, values stored in memory locations, and otherhardware components within such circuitry to implement thefunctions/acts specified in the block diagrams and/or flowchart block orblocks, and thereby create means (functionality) and/or structure forimplementing the functions/acts specified in the block diagrams and/orflowchart block(s).

These computer program instructions may also be stored in a tangiblecomputer-readable medium that can direct a computer or otherprogrammable data processing apparatus to function in a particularmanner, such that the instructions stored in the computer-readablemedium produce an article of manufacture including instructions whichimplement the functions/acts specified in the block diagrams and/orflowchart block or blocks.

A tangible, non-transitory computer-readable medium may include anelectronic, magnetic, optical, electromagnetic, or semiconductor datastorage system, apparatus, or device. More specific examples of thecomputer-readable medium would include the following: a portablecomputer diskette, a random access memory (RAM) circuit, a read-onlymemory (ROM) circuit, an erasable programmable read-only memory (EPROMor Flash memory) circuit, a portable compact disc read-only memory(CD-ROM), and a portable digital video disc read-only memory(DVD/BlueRay).

The computer program instructions may also be loaded onto a computerand/or other programmable data processing apparatus to cause a series ofoperational steps to be performed on the computer and/or otherprogrammable apparatus to produce a computer-implemented process suchthat the instructions which execute on the computer or otherprogrammable apparatus provide steps for implementing the functions/actsspecified in the block diagrams and/or flowchart block or blocks.Accordingly, embodiments of the present invention may be embodied inhardware and/or in software (including firmware, resident software,micro-code, etc.) that runs on a processor such as a digital signalprocessor, which may collectively be referred to as “circuitry,” “amodule” or variants thereof.

It should also be noted that in some alternate implementations, thefunctions/acts noted in the blocks may occur out of the order noted inthe flowcharts. For example, two blocks shown in succession may in factbe executed substantially concurrently or the blocks may sometimes beexecuted in the reverse order, depending upon the functionality/actsinvolved. Moreover, the functionality of a given block of the flowchartsand/or block diagrams may be separated into multiple blocks and/or thefunctionality of two or more blocks of the flowcharts and/or blockdiagrams may be at least partially integrated. Finally, other blocks maybe added/inserted between the blocks that are illustrated, and/orblocks/operations may be omitted without departing from the scope of theinvention. Moreover, although some of the diagrams include arrows oncommunication paths to show a primary direction of communication, it isto be understood that communication may occur in the opposite directionto the depicted arrows.

Many different embodiments have been disclosed herein, in connectionwith the above description and the drawings. It will be understood thatit would be unduly repetitious and obfuscating to literally describe andillustrate every combination and subcombination of these embodiments.Accordingly, the present specification, including the drawings, shall beconstrued to constitute a complete written description of variousexample combinations and subcombinations of embodiments and of themanner and process of making and using them, and shall support claims toany such combination or subcombination.

Many variations and modifications can be made to the embodiments withoutsubstantially departing from the principles of the present invention.All such variations and modifications are intended to be included hereinwithin the scope of the present invention. Accordingly, the abovedisclosed subject matter is to be considered illustrative, and notrestrictive, and the appended claims are intended to cover all suchmodifications, enhancements, and other embodiments, which fall withinthe spirit and scope of the present invention.

That which is claimed is:
 1. A method of operating a user equipmentcommunicating with a base station of a radio access network, the methodcomprising: selecting a multiple-input-multiple-output, MIMO, rank and aMIMO precoding entity from a codebook of MIMO precoding entities for adownlink communication from the base station to the user equipment;selecting a modulation/coding scheme to be mapped to first and secondMIMO layers of the downlink communication using the MIMO precodingentity; and communicating channel quality information identifying theMIMO precoding entity and the modulation/coding scheme from the userequipment to the base station.
 2. The method according to claim 1wherein the modulation/coding scheme comprises a first modulation/codingscheme, the method further comprising: responsive to selecting the MIMOprecoding entity, selecting a second modulation/coding scheme to bemapped to a third MIMO layer of the downlink communication using theMIMO precoding entity, wherein the channel quality information includesthe second modulation/coding scheme.
 3. The method according to claim 1wherein the modulation/coding scheme comprises a first modulation/codingscheme, the method further comprising: responsive to selecting the MIMOprecoding entity, selecting a second modulation/coding scheme to bemapped to third and fourth MIMO layers of the downlink communicationusing the MIMO precoding entity, wherein the channel quality informationincludes the second modulation/coding scheme.
 4. The method according toclaim 1 further comprising; providing estimates of the downlink channelresponsive to pilot signals received from the base station; andestimating respective first and second signal strengths for the firstand second layers of the MIMO precoding entity; wherein selecting themodulation/coding scheme comprises selecting the modulation/codingscheme responsive to a function of first and second signal strengths. 5.The method according to claim 4 wherein selecting the modulation/codingscheme comprises selecting the modulation/coding scheme responsive to anaverage of the first and second signal strengths.
 6. The methodaccording to claim 4 wherein selecting the modulation/coding schemecomprises selecting the modulation/coding scheme responsive to a maximumof the first and second signal strengths.
 7. The method according toclaim 4 wherein selecting the modulation/coding scheme comprisesselecting the modulation/coding scheme responsive to a minimum of thefirst and second signal strengths.
 8. The method according to claims 1further comprising: providing channel estimates for a downlink channelfrom the base station to the user equipment; estimating signal strengthsfor the MIMO layers for the precoding entities of the codebook using thechannel estimates; and estimating capacities for the precoding entitiesof the codebook using the signal strengths, wherein selecting the MIMOprecoding entity comprises selecting the MIMO precoding entityresponsive to the capacities; wherein selecting comprises selecting themodulation/coding scheme responsive to a function of first and secondsignal strengths estimated for the first and second MIMO layers for theprecoding entity using the channel estimates.
 9. The method according toclaim 8 wherein selecting the modulation/coding scheme comprisesselecting the modulation/coding scheme responsive to an average of thefirst and second signal strengths, responsive to a maximum of the firstand second signal strengths, and/or responsive to a minimum of the firstand second signal strengths.
 10. The method according to claims 1further comprising; selecting a respective modulation/coding scheme foreach of the layers of each of the MIMO precoding entities of thecodebook; calculating a respective layer efficiency for each of thelayers of each of the MIMO precoding entities of the codebook responsiveto the respective modulation/coding schemes; and providing a respectiveprecoding entity efficiency for each of the MIMO precoding entities ofthe codebook responsive to the layer efficiencies of the respective MIMOprecoding entities; wherein selecting the MIMO precoding entitycomprises selecting the MIMO precoding entity responsive to theprecoding entity efficiencies.
 11. The method of claim 10 whereinproviding the respective precoding entity efficiency for the selectedMIMO precoding entity comprises providing the respective precodingentity efficiency for the selected MIMO precoding entity responsive to afunction of first and second layer efficiencies for the first and secondMIMO layers of the selected MIMO precoding entity.
 12. The method ofclaim 11 wherein providing the respective precoding entity efficiencyfor the selected MIMO precoding entity responsive to a function of firstand second layer efficiencies comprises providing the respectiveprecoding entity efficiency responsive to a maximum of the first andsecond layer efficiencies.
 13. The method of claim 12 wherein selectingthe modulation/coding scheme to be mapped to the first and second MIMOlayers of the selected precoding entity comprises selecting one of afirst modulation/coding scheme of the first layer of the selected MIMOprecoding entity and a second modulation/coding scheme of the secondlayer of the selected MIMO precoding entity corresponding to the maximumof the first and second layer efficiencies.
 14. The method of claim 11wherein providing the respective precoding entity efficiency for theselected MIMO precoding entity responsive to a function of first andsecond layer efficiencies comprises providing the respective precodingentity efficiency responsive to a minimum of the first and second layerefficiencies.
 15. The method of claim 14 wherein selecting themodulation/coding scheme to be mapped to the first and second MIMOlayers of the selected precoding entity comprises selecting one of afirst modulation/coding scheme of the first layer of the selected MIMOprecoding entity and a second modulation/coding scheme of the secondlayer of the selected MIMO precoding entity corresponding to the minimumof the first and second layer efficiencies.
 16. The method according toclaims 10 further comprising: providing estimates of the downlinkchannel responsive to pilot signals received from the base station; andestimating a respective signal strength for each layer of each of theMIMO precoding entities of the codebook using the estimates of thedownlink channel; wherein selecting comprises selecting the respectivemodulation/coding scheme for each of the layers of each of the MIMOprecoding entities of the codebook responsive to the respective signalstrengths.
 17. User equipment configured to communicate with a basestation of a radio access network, the user equipment comprising: atransceiver configured to receive communications from the base stationand to transmit communications to the base station; and a processorcoupled to the transceiver, the processor being configured to select amultiple-input-multiple-output, MIMO, rank and a MIMO precoding entityfrom a codebook of MIMO precoding entities for a downlink communicationfrom the base station to the user equipment, to select amodulation/coding scheme to be mapped to first and second MIMO layers ofthe downlink communication using the MIMO precoding entity, and tocommunicate channel quality information identifying the MIMO precodingentity and the modulation/coding scheme through the transceiver to thebase station.
 18. The user equipment of claim 17 wherein the processoris further configured to provide estimates of the downlink channelresponsive to pilot signals received from the base station, to estimaterespective first and second signal strengths for the first and secondlayers of the MIMO precoding entity, and to select the modulation/codingscheme responsive to a function of first and second signal strengths.19. The user equipment of claim 17 wherein the processor is furtherconfigured to provide channel estimates for a downlink channel from thebase station to the user equipment, to estimate signal strengths for theMIMO layers for the precoding entities of the codebook using the channelestimates, to estimate capacities for the precoding entities of thecodebook using the signal strengths, to select the MIMO precoding entityresponsive to the capacities, and to select the modulation/coding schemeresponsive to a function of first and second signal strengths estimatedfor the first and second MIMO layers for the precoding entity using thechannel estimates.
 20. The user equipment of claim 17 wherein theprocessor is further configured to select a respective modulation/codingscheme for each of the layers of each of the MIMO precoding entities ofthe codebook, to calculate a respective layer efficiency for each of thelayers of each of the MIMO precoding entities of the codebook responsiveto the respective modulation/coding schemes, to provide a respectiveprecoding entity efficiency for each of the MIMO precoding entities ofthe codebook responsive to the layer efficiencies of the respective MIMOprecoding entities, and to select the MIMO precoding entity responsiveto the precoding entity efficiencies.